Catheter with multiple ultrasound radiating members

ABSTRACT

A method of delivery ultrasonic energy and a therapeutic compound to a treatment site and an ultrasonic catheter system are disclosed. The ultrasonic catheter system comprises a tubular body having a proximal end, a distal end and a treatment zone located between the distal end and the proximal end, a fluid delivery lumen, at least one ultrasound radiating element positioned in the treatment zone, wiring electrically coupled to the at least one ultrasound radiating element and extending through the tubular body and terminating at a connector, and a control system comprising external circuitry and an isolation pod that is configured to be electrically connected to the connector, the isolation pod being positioned between the tubular body and the external system and comprising an isolation barrier and circuitry for driving the ultrasound radiating element.

PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/762,254, filed Apr. 16, 2010, which is a divisional of U.S. patentapplication Ser. No. 11/643,471, filed Dec. 21, 2006, now U.S. Pat. No.7,727,178, which is a divisional of U.S. patent application Ser. No.10/309,388, filed Dec. 3, 2002, now U.S. Pat. No. 7,220,239, whichclaims the benefit of U.S. Provisional Patent Application No.60/336,744, filed Dec. 3, 2001, U.S. Provisional Patent Application No.60/336,630, filed Dec. 3, 2001, and U.S. Provisional Patent ApplicationNo. 60/394,093, filed Jul. 3, 2002. The entire disclosure of all ofthese priority documents is hereby incorporated by reference in itsentirety.

STATEMENT REGARDING FEDERALLY SPONSORED R&D

The invention was made with government support under Grant No. NIH R44HL057739 awarded by the National Institutes of Health. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an ultrasonic catheter andmore specifically to an ultrasonic catheter configured to deliverultrasonic energy and a therapeutic compound to a treatment site.

2. Description of the Related Art

Several medical applications use ultrasonic energy. For example, U.S.Pat. Nos. 4,821,740, 4,953,565 and 5,007,438 disclose the use ofultrasonic energy to enhance the effect of various therapeuticcompounds. An ultrasonic catheter can be used to deliver ultrasonicenergy and a therapeutic compound to a treatment site in a patient'sbody. Such an ultrasonic catheter typically includes an ultrasoundassembly configured to generate ultrasonic energy and a fluid deliverylumen for delivering the therapeutic compound to the treatment site.

As taught in U.S. Pat. No. 6,001,069, such ultrasonic catheters can beused to treat human blood vessels that have become partially orcompletely occluded by plaque, thrombi, emboli or other substances thatreduce the blood carrying capacity of the vessel. To remove or reducethe occlusion, the ultrasonic catheter is used to deliver solutionscontaining dissolution compounds directly to the occlusion site.Ultrasonic energy generated by the ultrasound assembly enhances thetherapeutic effect of the dissolution compounds. For example, in oneapplication of such an ultrasonic catheter, an ultrasound-enhancedthrombolytic therapy dissolves blood clots in arteries and veins in thetreatment of diseases such as peripheral arterial occlusion or deep veinthrombosis. In such applications, ultrasonic energy enhancesthrombolysis with agents such as urokinase, tissue plasminogen activator(“TPA”) and the like.

Ultrasonic catheters can also be used to enhance gene therapy at atreatment site within the patient's body. For example, U.S. Pat. No.6,135,976 discloses an ultrasonic catheter having one or more expandablesections capable of occluding a section of a body lumen, such as a bloodvessel. A gene therapy composition is then delivered to the occludedvessel through the catheter fluid delivery lumen. Ultrasonic energygenerated by the ultrasound assembly is applied to the occluded vessel,thereby enhancing the delivery of a genetic composition into the cellsof the occluded vessel.

Ultrasonic catheters can also be used to enhance delivery and activationof light activated drugs. For example, U.S. Pat. No. 6,176,842 disclosesmethods for using an ultrasonic catheter to treat biological tissues bydelivering a light activated drug to the biological tissues and exposingthe light activated drug to ultrasound energy.

SUMMARY OF THE INVENTION

In certain medical procedures, it is desirable to provide ultrasonicenergy along a substantial length of a body lumen. For example, longsegment peripheral arterial occlusions, such as those in the arteries ofthe leg, may have an axial length in the range of 10 to 50 cm. To date,it has been difficult to design an ultrasonic catheter capable ofefficiently applying ultrasound energy over such lengths.

One method for emitting ultrasonic energy over such lengths is toprovide the ultrasonic catheter with a plurality of ultrasonictransducers spaced along a distal region of the catheter. Such anarrangement faces several technical hurdles. For example, because theultrasonic transducers are relatively rigid, the catheter may become tooinflexible to be navigated through the lumens of the patient's body. Onesolution is to use smaller transducers. However, smaller transducers maynot be capable of producing sufficient energy at the proper frequency toenhance the therapeutic affect of a therapeutic agent.

Another solution is disclosed in U.S. Pat. No. 6,296,610. This patentdiscloses a catheter with a plurality of transducers that are moved backand forth within the catheter through the treatment zone. However, thisarrangement is generally undesirable because it requires a translationsystem for moving the ultrasonic elements within the catheter.

Additionally, for ease of manufacturing and reduced costs, it isgenerally desirable to use ultrasonic transducers that are in the formof rectangular bars as compared to, for example, cylindricaltransducers. However, such arrangements should still generate atherapeutically effective ultrasonic energy field.

A need, therefore, exists for an improved ultrasonic catheter capable ofproviding ultrasonic energy over a substantial length of a body lumenwith little or no movement of the ultrasonic elements within the patientduring treatment. Such a catheter preferably uses flat rectangularultrasonic transducers.

As such, according to one embodiment of the present invention, acatheter system for delivering ultrasonic energy and a therapeuticcompound to a treatment site within a body lumen comprises a tubularbody. The tubular body has a proximal end, a distal end and an energydelivery section positioned between the proximal end and the distal end.The catheter system further comprises a fluid delivery lumen extendingat least partially through the tubular body. The fluid delivery lumenhas at least one outlet in the energy delivery section. The cathetersystem further comprises an inner core configured for insertion into thetubular body. The inner core comprises an elongate electrical conductorhaving a plurality of flattened regions. Each flattened region has afirst flat side and a second flat side opposite the first flat side. Theinner core further comprises a plurality of ultrasound radiating membersmounted in pairs to the flattened regions of the elongate electricalconductor. A first ultrasound radiating member is mounted to the firstflat side of the elongate electrical conductor, and a second ultrasoundradiating member is mounted to the second flat side of the elongateelectrical conductor. The inner core further comprises wiring such thata voltage can be applied from the elongate electrical conductor acrossthe first and second ultrasound radiating members. The first and secondultrasound radiating members can be driven simultaneously.

According to another embodiment of the present invention, a cathetersystem for delivering ultrasonic energy to a treatment site comprises atubular body. The tubular body has a proximal end, a distal end and atreatment zone located between the distal end and the proximal end. Thecatheter system further comprises an ultrasonic assembly positionedwithin the treatment zone. The ultrasonic assembly comprises anelectrical conductor and an ultrasonic transducer pair. The ultrasonictransducer pair includes a first ultrasound transducer having a firstportion and a second ultrasound transducer having a second portion. Thefirst portion of the first transducer and the second portion of thesecond transducer face each other and are electrically coupled to theelectrical conductor.

According to another embodiment of the present invention, a cathetersystem for delivering ultrasonic energy to a treatment site comprises atubular body. The tubular body has a proximal end, a distal end and atreatment zone located between the distal and proximal ends. Thecatheter system further comprises an ultrasonic assembly positionedwithin the treatment zone. The ultrasonic assembly comprises anelectrical conductor and an ultrasonic transducer pair. The ultrasonictransducer pair includes a rectangular solid first ultrasonic elementand a rectangular solid second ultrasonic element. The first and secondultrasonic elements are mounted on opposite sides of the electricalconductor.

According to another embodiment of the present invention, an apparatuscomprises an elongate tubular body having a fluid delivery lumen. Theapparatus further comprises an inner core configured for insertion intothe tubular body. The inner core comprises a common wire and a pluralityof ultrasound radiating members. The plurality of ultrasound radiatingmembers are positioned and electrically coupled to the common wire inpairs. The apparatus further comprises a control system configured todrive each pair of ultrasound radiating members.

According to another embodiment of the present invention, a method ofdelivering ultrasonic energy and a therapeutic compound to a treatmentsite comprises providing a catheter with a plurality of ultrasoundradiating members. The plurality of ultrasound radiating members areallocated into electrical groups comprising more than one ultrasoundradiating member. The method further comprises independently drivingeach group of ultrasonic radiating members. The method further comprisesdelivering the therapeutic compound through the catheter to thetreatment site.

According to another embodiment of the present invention, an ultrasoniccatheter comprises a tubular body. The tubular body has a proximal end,a distal end and a treatment zone located between the distal end and theproximal end. The ultrasonic catheter further comprises a plurality offluid delivery lumens defined within the tubular body. The ultrasoniccatheter further comprises an inner core comprising at least oneultrasound radiating element. The ultrasonic catheter further comprisesa plurality of cooling fluid channels defined between at least an innersurface of the tubular body and an outer surface of the inner core. Eachcooling fluid channel is positioned generally radially between two fluiddelivery lumens.

According to another embodiment of the present invention, an ultrasoniccatheter system comprises a tubular body. The tubular body has aproximal end, a distal end and a treatment zone located between thedistal end and the proximal end. The ultrasonic catheter system furthercomprises a fluid delivery lumen. The ultrasonic catheter system furthercomprises at least one ultrasound radiating element positioned in thetreatment zone. The ultrasonic catheter system further comprises wiringelectrically coupled to the at least one ultrasound radiating element.The wiring extends through the tubular body and terminates at aconnector. The ultrasonic catheter system further comprises a controlsystem. The control system comprises external circuitry and an isolationpod. The isolation pod is configured to be electrically connected to theconnector. The isolation pod is also positioned between the tubular bodyand the external system. The isolation pod comprises an isolationbarrier and circuitry for driving the ultrasound radiating element.

According to another embodiment of the present invention, an ultrasoniccatheter comprises a tubular body. The tubular body has a proximal end,a distal end and a treatment zone located between the distal end and theproximal end. The ultrasonic catheter further comprises at least onefluid delivery lumen incorporated into the tubular body. The ultrasoniccatheter further comprises a plurality of ultrasound radiating membersmounted within an inner core. The inner core is positioned within thetubular body such that at least one of the ultrasound radiating membersis located within the treatment zone. The ultrasonic catheter furthercomprises means for independently driving each of the ultrasoundtransducers.

For purposes of summarizing the invention and the advantages achievedover the prior art, certain objects and advantages of the invention havebeen described above. It is to be understood that not necessarily allsuch objects or advantages may be achieved in accordance with anyparticular embodiment of the invention. Thus, for example, those skilledin the art will recognize that the invention may be embodied or carriedout in a manner that achieves or optimizes one advantage or group ofadvantages as taught herein without necessarily achieving other objectsor advantages as may be taught or suggested herein.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments of the presentinvention will become readily apparent to those skilled in the art fromthe following detailed description of the preferred embodiments havingreference to the attached figures, the invention not being limited toany particular preferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an ultrasonic catheter configuredfor insertion into large vessels of the human body.

FIG. 2 is a cross-sectional view of the ultrasonic catheter of FIG. 1taken along line 2-2.

FIG. 3 is a schematic illustration of an elongate inner core configuredto be positioned within the central lumen of the catheter illustrated inFIG. 2.

FIG. 4 is a cross-sectional view of the elongate inner core of FIG. 3taken along line 4-4.

FIG. 5 is a schematic wiring diagram illustrating a preferred techniquefor electrically connecting five groups of ultrasound radiating membersto form an ultrasound assembly.

FIG. 6 is a schematic wiring diagram illustrating a preferred techniquefor electrically connecting one of the groups of FIG. 5.

FIG. 7A is a schematic illustration of the ultrasound assembly of FIG. 5housed within the inner core of FIG. 4.

FIG. 7B is a cross-sectional view of the ultrasound assembly of FIG. 7Ataken along line 7B-7B.

FIG. 7C is a cross-sectional view of the ultrasound assembly of FIG. 7Ataken along line 7C-7C.

FIG. 7D is a side view of an ultrasound assembly center wire twistedinto a helical configuration.

FIG. 8 illustrates the energy delivery section of the inner core of FIG.4 positioned within the energy delivery section of the tubular body ofFIG. 2.

FIG. 9 illustrates a wiring diagram for connecting a plurality oftemperature sensors with a common wire.

FIG. 10 is a block diagram of a feedback control system for use with anultrasonic catheter.

FIG. 11A is a side view of a treatment site.

FIG. 11B is a side view of the distal end of an ultrasonic catheterpositioned at the treatment site of FIG. 11A.

FIG. 11C is a cross-sectional view of the distal end of the ultrasoniccatheter of FIG. 11B positioned at the treatment site before atreatment.

FIG. 11D is a cross-sectional view of the distal end of the ultrasoniccatheter of FIG. 11C, wherein an inner core has been inserted into thetubular body to perform a treatment.

FIG. 12 is a circuit diagram of an isolation pod.

FIG. 13 illustrates the connection of ultrasound radiating memberswithin a catheter to an isolation pod.

FIG. 14 illustrates a selective activation of ultrasound radiatingmembers within a catheter.

FIG. 15 illustrates a second selective activation of ultrasoundradiating members within a catheter.

FIG. 16 illustrates a third selective activation of ultrasound radiatingmembers within a catheter.

FIG. 17 illustrates one embodiment for connecting ultrasound radiatingmembers within a catheter to an isolation pod.

FIG. 18 illustrates a second embodiment for connecting ultrasoundradiating members within a catheter to an isolation pod.

FIG. 19 illustrates the connection of temperature sensors within acatheter to an isolation pod.

FIG. 20 is a cross-sectional view of a catheter connector.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As described above, it is desired to provide an ultrasonic catheterhaving various features and advantages. Examples of such features andadvantages include the ability to apply ultrasonic energy to a treatmentsite. In another embodiments, the catheter has the ability to deliver atherapeutic compound to the treatment site. Preferred embodiments of anultrasonic catheter having certain of these features and advantages aredescribed herein. Methods of using such an ultrasonic catheter are alsodescribed herein.

The ultrasonic catheters described herein can be used to enhance thetherapeutic effects of therapeutic compounds at a treatment site withina patient's body. As used herein, the term “therapeutic compound” refersbroadly, without limitation, to a drug, medicament, dissolutioncompound, genetic material or any other substance capable of effectingphysiological functions. Additionally, any mixture comprising any suchsubstances is encompassed within this definition of “therapeuticcompound”, as well as any substance falling within the ordinary meaningof these terms. The enhancement of the effects of therapeutic compoundsusing ultrasonic energy is described in U.S. Pat. Nos. 5,318,014,5,362,309, 5,474,531, 5,628,728, 6,001,069 and 6,210,356, the entiredisclosure of which are hereby incorporated by herein by reference.Specifically, for applications that treat human blood vessels that havebecome partially or completely occluded by plaque, thrombi, emboli orother substances that reduce the blood carrying capacity of a vessel,suitable therapeutic compounds include, but are not limited to, anaqueous solution containing Heparin, Uronkinase, Streptokinase, TPA andBB-10153 (manufactured by British Biotech, Oxford, UK).

Certain features and aspects of the ultrasonic catheters disclosedherein may also find utility in applications where the ultrasonic energyitself provides a therapeutic effect. Examples of such therapeuticeffects include preventing or reducing stenosis and/or restenosis;tissue ablation, abrasion or disruption; promoting temporary orpermanent physiological changes in intracellular or intercellularstructures; and rupturing micro-balloons or micro-bubbles fortherapeutic compound delivery. Further information about such methodscan be found in U.S. Pat. Nos. 5,261,291 and 5,431,663, the entiredisclosure of which are hereby incorporated by herein by reference.

The ultrasonic catheters described herein are configured for applyingultrasonic energy over a substantial length of a body lumen, such as,for example, the larger vessels located in the leg. However, it shouldbe appreciated that certain features and aspects of the presentinvention may be applied to catheters configured to be inserted into thesmall cerebral vessels, in solid tissues, in duct systems and in bodycavities. Additional embodiments that may be combined with certainfeatures and aspects of the embodiments described herein are describedin U.S. patent application, Attorney Docket EKOS.026A, entitled“Ultrasound Assembly For Use With A Catheter” and filed Nov. 7, 2002,the entire disclosure of which is hereby incorporated herein byreference.

With initial reference to FIG. 1 schematically illustrates an ultrasoniccatheter 10 configured for use in the large vessels of a patient'sanatomy. For example, the ultrasonic catheter 10 illustrated in FIG. 1can be used to treat long segment peripheral arterial occlusions, suchas those in the vascular system of the leg.

As illustrated in FIG. 1, the ultrasonic catheter 10 generally comprisesa multi-component, elongate flexible tubular body 12 having a proximalregion 14 and a distal region 15. The tubular body 12 includes aflexible energy delivery section 18 located in the distal region 15 ofthe catheter 10. The tubular body 12 and other components of thecatheter 10 can be manufactured in accordance with any of a variety oftechniques well known in the catheter manufacturing field. Suitablematerials and dimensions can be readily selected based on the naturaland anatomical dimensions of the treatment site and on the desiredpercutaneous access site.

For example, in a preferred embodiment the proximal region 14 of thetubular body 12 comprises a material that has sufficient flexibility,kink resistance, rigidity and structural support to push the energydelivery section 18 through the patient's vasculature to a treatmentsite. Examples of such materials include, but are not limited to,extruded polytetrafluoroethylene (“PTFE”), polyethylenes (“PE”),polyamides and other similar materials. In certain embodiments, theproximal region 14 of the tubular body 12 is reinforced by braiding,mesh or other constructions to provide increased kink resistance andpushability. For example, nickel titanium or stainless steel wires canbe placed along or incorporated into the tubular body 12 to reducekinking.

In an embodiment configured for treating thrombus in the arteries of theleg, the tubular body 12 has an outside diameter between about 0.060inches and about 0.075 inches. In another embodiment, the tubular body12 has an outside diameter of about 0.071 inches. In certainembodiments, the tubular body 12 has an axial length of approximately105 centimeters, although other lengths may by appropriate for otherapplications.

The energy delivery section 18 of the tubular body 12 preferablycomprises a material that is thinner than the material comprising theproximal region 14 of the tubular body 12 or a material that has agreater acoustic transparency. Thinner materials generally have greateracoustic transparency than thicker materials. Suitable materials for theenergy delivery section 18 include, but are not limited to, high or lowdensity polyethylenes, urethanes, nylons, and the like. In certainmodified embodiments, the energy delivery section 18 may be formed fromthe same material or a material of the same thickness as the proximalregion 18.

In certain embodiments, the tubular body 12 is divided into at leastthree sections of varying stiffness. The first section, which preferablyincludes the proximal region 14, has a relatively higher stiffness. Thesecond section, which is located in an intermediate region between theproximal region 14 and the distal region 15 of the tubular body 12, hasa relatively lower stiffness. This configuration further facilitatesmovement and placement of the catheter 10. The third section, whichpreferably includes the energy delivery section 18, is generally lowerstiffness than the second section in spite of the presence of theultrasound radiating members 40.

FIG. 2 illustrates a cross section of the tubular body 12 taken alongline 2-2 in FIG. 1. In the embodiment illustrated in FIG. 2, three fluiddelivery lumens 30 are incorporated into the tubular body 12. In otherembodiments, more or fewer fluid delivery lumens can be incorporatedinto the tubular body 12. The arrangement of the fluid delivery lumens30 preferably provides a hollow central lumen 51 passing through thetubular body 12. The cross-section of the tubular body 12, asillustrated in FIG. 2, is preferably substantially constant along thelength of the catheter 10. Thus, in such embodiments, substantially thesame cross-section is present in both the proximal region 14 and thedistal region 15 of the catheter 10, including the energy deliverysection 18.

In certain embodiments, the central lumen 51 has a minimum diametergreater than about 0.030 inches. In another embodiment, the centrallumen 51 has a minimum diameter greater than about 0.037 inches. In onepreferred embodiment, the fluid delivery lumens 30 have dimensions ofabout 0.026 inches wide by about 0.0075 inches high, although otherdimensions may be used in other applications.

As described above, the central lumen 51 preferably extends through thelength of the tubular body 12. As illustrated in FIG. 1, the centrallumen 51 preferably has a distal exit port 29 and a proximal access port31. The proximal access port 31 forms part of the backend hub 33, whichis attached to the proximal region 14 of the catheter 10. The backendhub preferably further comprises cooling fluid fitting 46, which ishydraulically connected to the central lumen 51. The backend hub 33 alsopreferably comprises a therapeutic compound inlet port 32, which is inhydraulic connection with the fluid delivery lumens 30, and which can behydraulically coupled to a source of therapeutic compound via a hub suchas a Luer fitting.

The central lumen 51 is configured to receive an elongate inner core 34of which a preferred embodiment is illustrated in FIG. 3. The elongateinner core 34 preferably comprises a proximal region 36 and a distalregion 38. Proximal hub 37 is fitted on the inner core 34 at one end ofthe proximal region 36. One or more ultrasound radiating members arepositioned within an inner core energy delivery section 41 locatedwithin the distal region 38. The ultrasound radiating members 40 form anultrasound assembly 42, which will be described in detail below.

As shown in the cross-section illustrated in FIG. 4, which is takenalong lines 4-4 in FIG. 3, the inner core 34 preferably has acylindrical shape, with an outer diameter that permits the inner core 34to be inserted into the central lumen 51 of the tubular body 12 via theproximal access port 31. Suitable outer diameters of the inner core 34include, but are not limited to, about 0.010 inches to about 0.100inches. In another embodiment, the outer diameter of the inner core 34is between about 0.020 inches and about 0.080 inches. In yet anotherembodiment, the inner core 34 has an outer diameter of about 0.035inches.

Still referring to FIG. 4, the inner core 34 preferably comprises acylindrical outer body 35 that houses the ultrasound assembly 42. Theultrasound assembly 42 comprises wiring and ultrasound radiatingmembers, described in greater detail in FIGS. 5 through 7D, such thatthe ultrasound assembly 42 is capable of radiating ultrasonic energyfrom the energy delivery section 41 of the inner core 34. The ultrasoundassembly 42 is electrically connected to the backend hub 33, where theinner core 34 can be connected to a control system 100 via cable 45(illustrated in FIG. 1). Preferably, an electrically insulating pottingmaterial 43 fills the inner core 34, surrounding the ultrasound assembly42, thus preventing movement of the ultrasound assembly 42 with respectto the outer body 35. In one embodiment, the thickness of the outer body35 is between about 0.0002 inches and 0.010 inches. In anotherembodiment, the thickness of the outer body 35 is between about 0.0002inches and 0.005 inches. In yet another embodiment, the thickness of theouter body 35 is about 0.0005 inches.

In a preferred embodiment, the ultrasound assembly 42 comprises aplurality of ultrasound radiating members 40 that are divided into oneor more groups. For example, FIGS. 5 and 6 are schematic wiring diagramsillustrating one technique for connecting five groups of ultrasoundradiating members 40 to form the ultrasound assembly 42. As illustratedin FIG. 5, the ultrasound assembly 42 comprises five groups G1, G2, G3,G4, G5 of ultrasound radiating members 40 that are electricallyconnected to each other. The five groups are also electrically connectedto the control system 100.

As used herein, the terms “ultrasonic energy”, “ultrasound” and“ultrasonic” are broad terms, having their ordinary meanings, andfurther refer to, without limitation, mechanical energy transferredthrough longitudinal pressure or compression waves. Ultrasonic energycan be emitted as continuous or pulsed waves, depending on therequirements of a particular application. Additionally, ultrasonicenergy can be emitted in waveforms having various shapes, such assinusoidal waves, triangle waves, square waves, or other wave forms.Ultrasonic energy includes sound waves. In certain embodiments, theultrasonic energy has a frequency between about 20 kHz and about 20 MHz.For example, in one embodiment, the waves have a frequency between about500 kHz and about 20 MHz. In another embodiment, the waves have afrequency between about 1 MHz and about 3 MHz. In yet anotherembodiment, the waves have a frequency of about 2 MHz. The averageacoustic power is between about 0.01 watts and 300 watts. In oneembodiment, the average acoustic power is about 15 watts.

As used herein, the term “ultrasound radiating member” refers to anyapparatus capable of producing ultrasonic energy. For example, in oneembodiment, an ultrasound radiating member comprises an ultrasonictransducer, which converts electrical energy into ultrasonic energy. Asuitable example of an ultrasonic transducer for generating ultrasonicenergy from electrical energy includes, but is not limited to,piezoelectric ceramic oscillators. Piezoelectric ceramics typicallycomprise a crystalline material, such as quartz, that change shape whenan electrical current is applied to the material. This change in shape,made oscillatory by an oscillating driving signal, creates ultrasonicsound waves. In other embodiments, ultrasonic energy can be generated byan ultrasonic transducer that is remote from the ultrasound radiatingmember, and the ultrasonic energy can be transmitted, via, for example,a wire that is coupled to the ultrasound radiating member.

Still referring to FIG. 5, the control circuitry 100 preferablycomprises, among other things, a voltage source 102. The voltage source102 comprises a positive terminal 104 and a negative terminal 106. Thenegative terminal 106 is connected to common wire 108, which connectsthe five groups G1-G5 of ultrasound radiating members 40 in series. Thepositive terminal 104 is connected to a plurality of lead wires 110,which each connect to one of the five groups G1-G5 of ultrasoundradiating members 40. Thus, under this configuration, each of the fivegroups G1-G5, one of which is illustrated in FIG. 6, is connected to thepositive terminal 104 via one of the lead wires 110, and to the negativeterminal 106 via the common wire 108.

Referring now to FIG. 6, each group G1-G5 comprises a plurality ofultrasound radiating members 40. Each of the ultrasound radiatingmembers 40 is electrically connected to the common wire 108 and to thelead wire 310 via one of two positive contact wires 112. Thus, whenwired as illustrated, a constant voltage difference will be applied toeach ultrasound radiating member 40 in the group. Although the groupillustrated in FIG. 6 comprises twelve ultrasound radiating members 40,one of ordinary skill in the art will recognize that more or fewerultrasound radiating members 40 can be included in the group. Likewise,more or fewer than five groups can be included within the ultrasoundassembly 42 illustrated in FIG. 5.

FIG. 7A illustrates one preferred technique for arranging the componentsof the ultrasound assembly 42 (as schematically illustrated in FIG. 5)into the inner core 34 (as schematically illustrated in FIG. 4). FIG. 7Ais a cross-sectional view of the ultrasound assembly 42 taken withingroup G1 in FIG. 5, as indicated by the presence of four lead wires 110.For example, if a cross-sectional view of the ultrasound assembly 42 wastaken within group G4 in FIG. 5, only one lead wire 310 would be present(that is, the one lead wire connecting group G5).

Referring still to FIG. 7A, the common wire 108 comprises an elongate,flat piece of electrically conductive material in electrical contactwith a pair of ultrasound radiating members 40. Each of the ultrasoundradiating members 40 is also in electrical contact with a positivecontact wire 312. Because the common wire 108 is connected to thenegative terminal 106, and the positive contact wire 312 is connected tothe positive terminal 104, a voltage difference can be created acrosseach ultrasound radiating member 40. Lead wires 110 are preferablyseparated from the other components of the ultrasound assembly 42, thuspreventing interference with the operation of the ultrasound radiatingmembers 40 as described above. For example, in one preferred embodiment,the inner core 34 is filled with an insulating potting material 43, thusdeterring unwanted electrical contact between the various components ofthe ultrasound assembly 42.

FIGS. 7B and 7C illustrate cross sectional views of the inner core 34 ofFIG. 7A taken along lines 7B-7B and 7C-7C, respectively. As illustratedin FIG. 7B, the ultrasound radiating members 40 are mounted in pairsalong the common wire 108. The ultrasound radiating members 40 areconnected by positive contact wires 112, such that substantially thesame voltage is applied to each ultrasound radiating member 40. Asillustrated in FIG. 7C, the common wire 108 preferably comprises wideregions 108W upon which the ultrasound radiating members 40 can bemounted, thus reducing the likelihood that the paired ultrasoundradiating members 40 will short together. In certain embodiments,outside the wide regions 108W, the common wire 108 may have a moreconventional, rounded wire shape.

In a modified embodiment, such as illustrated in FIG. 7D, the commonwire 108 is twisted to form a helical shape before being fixed withinthe inner core 34. In such embodiments, the ultrasound radiating members40 are oriented in a plurality of radial directions, thus enhancing theradial uniformity of the resulting ultrasonic energy field.

One of ordinary skill in the art will recognize that the wiringarrangement described above can be modified to allow each group G1, G2,G3, G4, G5 to be independently powered. Specifically, by providing aseparate power source within the control system 100 for each group, eachgroup can be individually turned on or off, or can be driven with anindividualized power. This provides the advantage of allowing thedelivery of ultrasonic energy to be “turned off” in regions of thetreatment site where treatment is complete, thus preventing deleteriousor unnecessary ultrasonic energy to be applied to the patient.

The embodiments described above, and illustrated in FIGS. 5 through 7,illustrate a plurality of ultrasound radiating members groupedspatially. That is, in such embodiments, all of the ultrasound radiatingmembers within a certain group are positioned adjacent to each other,such that when a single group is activated, ultrasonic energy isdelivered at a specific length of the ultrasound assembly. However, inmodified embodiments, the ultrasound radiating members of a certaingroup may be spaced apart from each other, such that the ultrasoundradiating members within a certain group are not positioned adjacent toeach other. In such embodiments, when a single group is activated,ultrasonic energy can be delivered from a larger, spaced apart portionof the energy delivery section. Such modified embodiments may beadvantageous in applications wherein it is desired to deliver a lessfocussed, more diffuse ultrasonic energy field to the treatment site.

In a preferred embodiment, the ultrasound radiating members 40 compriserectangular lead zirconate titanate (“PZT”) ultrasound transducers thathave dimensions of about 0.017 inches by about 0.010 inches by about0.080 inches. In other embodiments, other configuration may be used. Forexample, disc-shaped ultrasound radiating members 40 can be used inother embodiments. In a preferred embodiment, the common wire 108comprises copper, and is about 0.005 inches thick, although otherelectrically conductive materials and other dimensions can be used inother embodiments. Lead wires 110 are preferably 36 gauge electricalconductors, while positive contact wires 112 are preferably 42 gaugeelectrical conductors. However, one of ordinary skill in the art willrecognize that other wire gauges can be used in other embodiments.

As described above, suitable frequencies for the ultrasound radiatingmember 40 include, but are not limited to, from about 20 kHz to about 20MHz. In one embodiment, the frequency is between about 500 kHz and 20MHz, and in another embodiment 1 MHz and 3 MHz. In yet anotherembodiment, the ultrasound radiating members 40 are operated with afrequency of about 2 MHz.

FIG. 8 illustrates the inner core 34 positioned within the tubular body12. Details of the ultrasound assembly 42, provided in FIG. 7A, areomitted for clarity. As described above, the inner core 34 can be slidwithin the central lumen 51 of the tubular body 12, thereby allowing theinner core energy delivery section 41 to be positioned within thetubular body energy delivery section 18. For example, in a preferredembodiment, the materials comprising the inner core energy deliverysection 41, the tubular body energy delivery section 18, and the pottingmaterial 43 all comprise materials having a similar acoustic impedance,thereby minimizing ultrasonic energy losses across material interfaces.

FIG. 8 further illustrates placement of fluid delivery ports 58 withinthe tubular body energy delivery section 18. As illustrated, holes orslits are formed from the fluid delivery lumen 30 through the tubularbody 12, thereby permitting fluid flow from the fluid delivery lumen 30to the treatment site. Thus, a source of therapeutic compound coupled tothe inlet port 32 provides a hydraulic pressure which drives thetherapeutic compound through the fluid delivery lumens 30 and out thefluid delivery ports 58.

By evenly spacing the fluid delivery lumens 30 around the circumferenceof the tubular body 12, as illustrated in FIG. 8, a substantially evenflow of therapeutic compound around the circumference of the tubularbody 12 can be achieved. In addition, the size, location and geometry ofthe fluid delivery ports 58 can be selected to provide uniform fluidflow from the fluid delivery ports 30 to the treatment site. Forexample, in one embodiment, fluid delivery ports closer to the proximalregion of the energy delivery section 18 have smaller diameters thenfluid delivery closer to the distal region of the energy deliverysection 18, thereby allowing uniform delivery of fluid across the entireenergy delivery section.

For example, in one embodiment in which the fluid delivery ports 58 havesimilar sizes along the length of the tubular body 12, the fluiddelivery ports 58 have a diameter between about 0.0005 inches to about0.0050 inches. In another embodiment in which the size of the fluiddelivery ports 58 changes along the length of the tubular body 12, thefluid delivery ports 58 have a diameter between about 0.001 inches toabout 0.005 inches in the proximal region of the energy delivery section18, and between about 0.005 inches to 0.0020 inches in the distal regionof the energy delivery section 18. The increase in size between adjacentfluid delivery ports 58 depends on the material comprising the tubularbody 12, and on the size of the fluid delivery lumen 30. The fluiddelivery ports 58 can be created in the tubular body 12 by punching,drilling, burning or ablating (such as with a laser), or by any othersuitable method. Therapeutic compound flow along the length of thetubular body 12 can also be increased by increasing the density of thefluid delivery ports 58 toward the distal region 15 of the tubular body12.

It should be appreciated that it may be desirable to provide non-uniformfluid flow from the fluid delivery ports 58 to the treatment site. Insuch embodiment, the size, location and geometry of the fluid deliveryports 58 can be selected to provide such non-uniform fluid flow.

Referring still to FIG. 8, placement of the inner core 34 within thetubular body 12 further defines cooling fluid lumens 44. Cooling fluidlumens 44 are formed between an outer surface 39 of the inner core 34and an inner surface 16 of the tubular body 12. In certain embodiments,a cooling fluid can is introduced through the proximal access port 31such that cooling fluid flow is produced through cooling fluid lumens 44and out distal exit port 29 (see FIG. 1). The cooling fluid lumens 44are preferably evenly spaced around the circumference of the tubularbody 12 (that is, at approximately 120° increments for a three-lumenconfiguration), thereby providing uniform cooling fluid flow over theinner core 34. Such a configuration is desirably to remove unwantedthermal energy at the treatment site. As will be explained below, theflow rate of the cooling fluid and the power to the ultrasound assembly42 can be adjusted to maintain the temp of the inner core energydelivery section 41 within a desired range.

In a preferred embodiment, the inner core 34 can be rotated or movedwithin the tubular body 12. Specifically, movement of the inner core 34can be accomplished by maneuvering the proximal hub 37 while holding thebackend hub 33 stationary. The inner core outer body 35 is at leastpartially constructed from a material that provides enough structuralsupport to permit movement of the inner core 34 within the tubular body12 without kinking of the tubular body 12. Additionally, the inner coreouter body 35 preferably comprises a material having the ability totransmit torque. Suitable materials for the inner core outer body 35include, but are not limited to, polyimides, polyesters, polyurethanes,thermoplastic elastomers and braided polyimides.

In a preferred embodiment, the fluid delivery lumens 30 and the coolingfluid lumens 44 are open at the distal end of the tubular body 12,thereby allowing the therapeutic compound and the cooling fluid to passinto the patient's vasculature at the distal exit port. Or, if desired,the fluid delivery lumens 30 can be selectively occluded at the distalend of the tubular body 12, thereby providing additional hydraulicpressure to drive the therapeutic compound out of the fluid deliveryports 58. In either configuration, the inner core 34 can prevented frompassing through the distal exit port by making providing the inner core34 with a length that is less than the length of the tubular body. Inother embodiments, a protrusion is formed on the internal side of thetubular body in the distal region 15, thereby preventing the inner core34 from passing through the distal exit port.

In still other embodiments, the catheter 10 further comprises anocclusion device (not shown) positioned at the distal exit port 29. Theocclusion device preferably has a reduced inner diameter that canaccommodate a guidewire, but that is less than the inner diameter of thecentral lumen 51. Thus, the inner core 34 is prevented from extendingthrough the occlusion device and out the distal exit port 29. Forexample, suitable inner diameters for the occlusion device include, butare not limited to, about 0.005 inches to about 0.050 inches. In otherembodiments, the occlusion device has a closed end, thus preventingcooling fluid from leaving the catheter 10, and instead recirculating tothe proximal region 14 of the tubular body 12. These and other coolingfluid flow configurations permit the power provided to the ultrasoundassembly 42 to be increased in proportion to the cooling fluid flowrate. Additionally, certain cooling fluid flow configurations can reduceexposure of the patient's body to cooling fluids.

In certain embodiments, as illustrated in FIG. 8, the tubular body 12further comprises one or more temperature sensors 20, which arepreferably located within the energy delivery section 18. In suchembodiments, the proximal region 14 of the tubular body 12 includes atemperature sensor lead which can be incorporated into cable 45(illustrated in FIG. 1). Suitable temperature sensors include, but arenot limited to, temperature sensing diodes, thermistors, thermocouples,resistance temperature detectors (“RTDs”) and fiber optic temperaturesensors which use thermalchromic liquid crystals. Suitable temperaturesensor 20 geometries include, but are not limited to, a point, a patchor a stripe. The temperature sensors 20 can be positioned within one ormore of the fluid delivery lumens 30 (as illustrated), and/or within oneor more of the cooling fluid lumens 44.

FIG. 9 illustrates one embodiment for electrically connecting thetemperature sensors 20. In such embodiments, each temperature sensor 20is coupled to a common wire 61 and is associated with an individualreturn wire 62. Accordingly, n+1 wires can be used to independentlysense the temperature at n distinct temperature sensors 20. Thetemperature at a particular temperature sensor 20 can be determined byclosing a switch 64 to complete a circuit between that thermocouple'sindividual return wire 62 and the common wire 61. In embodiments whereinthe temperature sensors 20 comprise thermocouples, the temperature canbe calculated from the voltage in the circuit using, for example, asensing circuit 63, which can be located within the external controlcircuitry 100.

In other embodiments, each temperature sensor 20 is independently wired.In such embodiments, 2n wires through the tubular body 12 toindependently sense the temperature at n independent temperature sensors20. In still other embodiments, the flexibility of the tubular body 12can be improved by using fiber optic based temperature sensors 20. Insuch embodiments, flexibility can be improved because only n fiber opticmembers are used to sense the temperature at n independent temperaturesensors 20.

FIG. 10 illustrates one embodiment of a feedback control system 68 thatcan be used with the catheter 10. The feedback control system 68 can beintegrated into the control system that is connected to the inner core34 via cable 45 (as illustrated in FIG. 1). The feedback control system68 allows the temperature at each temperature sensor 20 to be monitoredand allows the output power of the energy source 70 to be adjustedaccordingly. A physician can, if desired, override the closed or openloop system.

The feedback control system 68 preferably comprises an energy source 70,power circuits 72 and a power calculation device 74 that is coupled tothe ultrasound radiating members 40. A temperature measurement device 76is coupled to the temperature sensors 20 in the tubular body 12. Aprocessing unit 78 is coupled to the power calculation device 74, thepower circuits 72 and a user interface and display 80.

In operation, the temperature at each temperature sensor 20 isdetermined by the temperature measurement device 76. The processing unit78 receives each determined temperature from the temperature measurementdevice 76. The determined temperature can then be displayed to the userat the user interface and display 80.

The processing unit 78 comprises logic for generating a temperaturecontrol signal. The temperature control signal is proportional to thedifference between the measured temperature and a desired temperature.The desired temperature can be determined by the user (at set at theuser interface and display 80) or can be preset within the processingunit 78.

The temperature control signal is received by the power circuits 72. Thepower circuits 72 are preferably configured to adjust the power level,voltage, phase and/or current of the electrical energy supplied to theultrasound radiating members 40 from the energy source 70. For example,when the temperature control signal is above a particular level, thepower supplied to a particular group of ultrasound radiating members 40is preferably reduced in response to that temperature control signal.Similarly, when the temperature control signal is below a particularlevel, the power supplied to a particular group of ultrasound radiatingmembers 40 is preferably increased in response to that temperaturecontrol signal. After each power adjustment, the processing unit 78preferably monitors the temperature sensors 20 and produces anothertemperature control signal which is received by the power circuits 72.

The processing unit 78 preferably further comprises safety controllogic. The safety control logic detects when the temperature at atemperature sensor 20 has exceeded a safety threshold. The processingunit 78 can then provide a temperature control signal which causes thepower circuits 72 to stop the delivery of energy from the energy source70 to that particular group of ultrasound radiating members 40.

Because, in certain embodiments, the ultrasound radiating members 40 aremobile relative to the temperature sensors 20, it can be unclear whichgroup of ultrasound radiating members 40 should have a power, voltage,phase and/or current level adjustment. Consequently, each group ofultrasound radiating member 40 can be identically adjusted in certainembodiments. In a modified embodiment, the power, voltage, phase, and/orcurrent supplied to each group of ultrasound radiating members 40 isadjusted in response to the temperature sensor 20 which indicates thehighest temperature. Making voltage, phase and/or current adjustments inresponse to the temperature sensed by the temperature sensor 20indicating the highest temperature can reduce overheating of thetreatment site.

The processing unit 78 also receives a power signal from a powercalculation device 74. The power signal can be used to determine thepower being received by each group of ultrasound radiating members 40.The determined power can then be displayed to the user on the userinterface and display 80.

As described above, the feedback control system 68 can be configured tomaintain tissue adjacent to the energy delivery section 18 below adesired temperature. For example, it is generally desirable to preventtissue at a treatment site from increasing more than 6° C. As describedabove, the ultrasound radiating members 40 can be electrically connectedsuch that each group of ultrasound radiating members 40 generates anindependent output. In certain embodiments, the output from the powercircuit maintains a selected energy for each group of ultrasoundradiating members 40 for a selected length of time.

The processing unit 78 can comprise a digital or analog controller, suchas for example a computer with software. When the processing unit 78 isa computer it can include a central processing unit (“CPU”) coupledthrough a system bus. As is well known in the art, the user interfaceand display 80 can comprise a mouse, a keyboard, a disk drive, a displaymonitor, a nonvolatile memory system, or any another. Also preferablycoupled to the bus is a program memory and a data memory.

In lieu of the series of power adjustments described above, a profile ofthe power to be delivered to each group of ultrasound radiating members40 can be incorporated into the processing unit 78, such that a presetamount of ultrasonic energy to be delivered is pre-profiled. In suchembodiments, the power delivered to each group of ultrasound radiatingmembers 40 can then be adjusted according to the preset profiles.

The ultrasound radiating members are preferably operated in a pulsedmode. For example, in one embodiment, the time average power supplied tothe ultrasound radiating members is preferably between about 0.1 wattsand 2 watts and more preferably between about 0.5 watts and 1.5 watts.In certain preferred embodiments, the time average power isapproximately 0.6 watts or 1.2 watts. The duty cycle is preferablybetween about 1% and 50% and more preferably between about 5% and 25%.In certain preferred embodiments, the duty ratio is approximately 7.5%or 15%. The pulse averaged power is preferably between about 0.1 wattsand 20 watts and more preferably between approximately 5 watts and 20watts. In certain preferred embodiments, the pulse averaged power isapproximately 8 watts and 16 watts. The amplitude during each pulse canbe constant or varied.

In one embodiment, the pulse repetition rate is preferably between about5 Hz and 150 Hz and more preferably between about 10 Hz and 50 Hz. Incertain preferred embodiments, the pulse repetition rate isapproximately 30 Hz. The pulse duration is preferably between about 1millisecond and 50 milliseconds and more preferably between about 1millisecond and 25 milliseconds. In certain preferred embodiments, thepulse duration is approximately 2.5 milliseconds or 5 milliseconds.

In one particular embodiment, the transducers are operated at an averagepower of approximately 0.6 watts, a duty cycle of approximately 7.5%, apulse repetition rate of 30 Hz, a pulse average electrical power ofapproximately 8 watts and a pulse duration of approximately 2.5milliseconds.

The ultrasound radiating member used with the electrical parametersdescribed herein preferably has an acoustic efficiency greater than 50%and more preferably greater than 75%. The ultrasound radiating membercan be formed a variety of shapes, such as, cylindrical (solid orhollow), flat, bar, triangular, and the like. The length of theultrasound radiating member is preferably between about 0.1 cm and about0.5 cm. The thickness or diameter of the ultrasound radiating members ispreferably between about 0.02 cm and about 0.2 cm.

FIGS. 11A through 11D illustrate a method for using the ultrasoniccatheter 10. As illustrated in FIG. 11A, a guidewire 84 similar to aguidewire used in typical angioplasty procedures is directed through apatient's vessels 86 to a treatment site 88 which includes a clot 90.The guidewire 84 is directed through the clot 90. Suitable vessels 86include, but are not limited to, the large periphery blood vessels ofthe body. Additionally, as mentioned above, the ultrasonic catheter 10also has utility in various imaging applications or in applications fortreating and/or diagnosing other diseases in other body parts.

As illustrated in FIG. 10B, the tubular body 12 is slid over and isadvanced along the guidewire 84 using conventional over-the-guidewiretechniques. The tubular body 12 is advanced until the energy deliverysection 18 of the tubular body 12 is positioned at the clot 90. Incertain embodiments, radiopaque markers (not shown) are positioned alongthe energy delivery section 18 of the tubular body 12 to aid in thepositioning of the tubular body 12 within the treatment site 88.

As illustrated in FIG. 10C, the guidewire 84 is then withdrawn from thetubular body 12 by pulling the guidewire 84 from the proximal region 14of the catheter 10 while holding the tubular body 12 stationary. Thisleaves the tubular body 12 positioned at the treatment site 88.

As illustrated in FIG. 10D, the inner core 34 is then inserted into thetubular body 12 until the ultrasound assembly 42 abuts against theocclusion device and is positioned at least partially within the energydelivery section 18 of the tubular body 12. Once the inner core 34 isproperly positioned, the ultrasound assembly 42 is activated to deliverultrasonic energy through the energy delivery section 18 to the clot 90.As described above, suitable ultrasonic energy is delivered with afrequency between about 20 kHz and about 20 MHz.

In a certain embodiment, the ultrasound assembly 42 comprises sixtyultrasound radiating members 40 spaced over a length of approximately 30to 50 cm. In such embodiments, the catheter 10 can be used to treat anelongate clot 90 without requiring movement of or repositioning of thecatheter 10 during the treatment. However, it will be appreciated thatin modified embodiments the inner core 34 can be moved or rotated withinthe tubular body 12 during the treatment. Such movement can beaccomplished by maneuvering the proximal hub 37 of the inner core 34while holding the backend hub 33 stationary.

Referring again to FIG. 11D, arrows 48 indicate that a cooling fluidflows through the cooling fluid lumen 44 and out the distal exit port29. Likewise, arrows 49 indicated that a therapeutic compound flowsthrough the fluid delivery lumen 30 and out the fluid delivery ports 58to the treatment site 88.

The cooling fluid can be delivered before, after, during orintermittently with the delivery of ultrasonic energy. Similarly, thetherapeutic compound can be delivered before, after, during orintermittently with the delivery of ultrasonic energy. Consequently, thesteps illustrated in FIGS. 11A through 11D can be performed in a varietyof different orders than that described above. The therapeutic compoundand ultrasonic energy are preferably applied until the clot 90 ispartially or entirely dissolved. Once the clot 90 has been dissolved tothe desired degree, the tubular body 12 and the inner core 34 arewithdrawn from the treatment site 88.

To reduce electric current leakage through the patient's body to ground,in certain embodiments the control system 100 may comprise an isolationpod 200. FIG. 12 illustrates one embodiment of an isolation pod 200 thatis contains certain portions of the control system 100, as described inmore detail below. Preferably, the external control circuitry 100,including the isolation pod 200 (if any), is positioned proximal to thebackend hub 33 (see FIG. 1), thereby preventing crosstalk between thewiring to the plurality of groups of ultrasound radiating members.

The isolation pod 200 comprises an isolation barrier 228 configured toreduce or eliminate unwanted electrical current flow through thepatient's body. For example, in the illustrated embodiment, twotransformers 256, 276 form an isolation barrier between the externalcontrol circuitry 100 and the certain components of the isolation pod200.

Referring still to FIG. 12, a transformer loop 278 is used to measurethe leakage current of the catheter 10. This leakage current representsthe current that does not return to the isolation pod 200 through thereturn lines, but instead passes through the patient's body to ground. Acenter tap from the transformer loop 278 connects to two diodes thatrectify the leakage current. In this example, zener diodes with a lowthreshold voltage are used to rectify the small signal provided from thetransformer loop.

The external control circuitry 100 provides a radio frequency signal 224for driving the ultrasound assembly 42. The radio frequency signal 224operates in the ultrasonic frequency range, and is tuned to a frequencythat activates the ultrasound radiating members 40 in the inner core 34.The radio frequency signal 224 is electromagnetically coupled to theisolation pod 200 using a transformer 256. The dielectric layers of thetransformer 256 form an isolation barrier. This isolation barriersubstantially prevents electrical current from flowing from theisolation pod 200, through the patient's body, and back into theisolation pod 200. By electromagnetically coupling the driving radiofrequency signal to the isolation pod 200, the current loop is brokenand electric current is thereby prevented from flowing through thepatient's body.

In the embodiment illustrated in FIG. 12, the isolation pod 200 iscompatible with multiple types of catheters. The different catheters canuse different types or quantities of ultrasound radiating members, whichin turn may cause variations in the input impedance seen by the radiofrequency amplifier. Even if the ultrasound radiating members areconfigured to be identical, fabrication defects will often cause theimpedance of ultrasound radiating members to vary. Additionally, theactivation pattern or configuration of ultrasound radiating memberswithin a catheter can also alter the input impedance.

The exemplary isolation pod 200 includes circuitry to enable matchingthe output impedance of the radio frequency amplifier to the inputimpedance of the ultrasound radiating members. For example, many radiofrequency amplifiers have an output impedance of about 50Ω. To maximizepower efficiency, the isolation pod 200 attempts to match the impedanceby providing a substantially equivalent 50Ω at the input.

Still referring to FIG. 12, the isolation pod 200 provides circuitry fortuning the input impedance of the isolation pod 200 to match the outputimpedance of the radio frequency amplifier. For example, FIG. 12illustrates the coupling transformer 256 with taps 258 on the secondaryside. Selecting different taps modifies the turns ratio of thetransformer and thereby changes the input impedance of the isolation pod200.

Changing the turns ratio of the coupling transformer 256 also affectsthe amplitude of the current passing through the ultrasonic assembly 42.As needed, the external control circuitry 100 compensates for thesechanges in amplitude for example by driving the radio frequency signalat different levels.

The embodiment illustrated in FIG. 12 also shows the use of inductors260 for tuning the input impedance. As illustrated, the isolation pod200 further comprises three individually controlled switches 262 thatconnect the three inductors with the radio frequency input circuit. Inthis example, a total of eight tuning settings are achievable by openingand closing the inductor switches in various combinations. The tuningcircuitry is not limited to the use of inductors or transformer taps.Other components, such as capacitors and resistors, may also be used totune the input impedance.

In one embodiment, tuning information is determined for a catheter atthe time of manufacture. The tuning information is then embedded intothe catheter, such as by saving the tuning information in anidentification programmable read-only memory (“PROM”) 254.Alternatively, the serial number or other identifying indicia of thecatheter together with the tuning information is entered into adatabase. The isolation pod 200 then retrieves the tuning informationfrom the database and appropriately adjusts the tuning circuitry to thecatheter that is attached to the isolation pod 200.

In another embodiment, the isolation pod 200 includes internal circuitryto detect the impedance of the ultrasound assembly 42 in the catheterand adjusts the tuning circuitry appropriately.

FIG. 12 further illustrates a configuration that is particularly adaptedfor the use of multiple ultrasound radiating members such as in thearrangements described above. In the illustrated embodiment, tenultrasound radiating members are connected to the isolation pod 200using five connections. The ultrasound radiating members are controlledby multiplexing the driving signal through five pairs of switches 268.The ultrasound radiating member driving lines in the inner core 34connect to the pairs of switches 268 within the isolation pod 200. Eachpair of switches 268 has four settings: (open, open), (open, closed),(closed, open) and (closed, closed). In operation, only three settingsare used because the (closed, closed) setting short-circuits the drivingsignal. In the illustrated example, wherein there are five ultrasoundradiating member driving lines, 3⁵=243 modes of operation are available.Examples of these modes are described in the embodiments that follow.

FIG. 13 illustrates an arrangement where the ultrasound radiatingmembers are linearly spaced within the catheter. In the illustratedexample, the catheter has five ultrasound radiating member driving lines302, 304, 306, 308, and 310.

In one embodiment, one pair of switches is in the (closed, open) settingand the remaining four pairs of switches are in the (open, closed)setting. In this such embodiments, four ultrasound radiating members areactive at a time. The remaining six ultrasound radiating members haveboth terminals short circuited, so they are not active.

FIG. 14 illustrates an embodiment wherein the pair of switches for thefirst ultrasound radiating member driving line 302 is in the (closed,open) setting and the pairs of switches for the remaining ultrasoundradiating member driving lines 304, 306, 308, 310 are in the (open,closed) setting. In this configuration, four ultrasound radiatingmembers 312, 314, 316, 318 are active, and six remaining ultrasoundradiating members 320, 322, 324, 326, 328, 330 are inactive. The activeultrasound radiating members 312, 314, 316, 318 have substantially thesame voltage differential appearing across the ultrasound radiatingmembers terminals.

FIG. 15 illustrates an embodiment wherein one pair of switches is in the(closed, open) setting and another pair of switches is in the (open,closed) setting. As illustrated, the pair of switches for the firstultrasound radiating member driving line 302 is in the (closed, open)setting, the pair of switches for the second ultrasound radiating memberdriving line 304 is in the (open, closed) setting, and the pairs ofswitches for the remaining ultrasound radiating member driving lines306, 308, 310 are in the (open, open) setting. The resulting network ofconnections between the ultrasound radiating member form several voltagedividers. This results in different voltage differences across theterminals of the various ultrasound radiating members. Assuming theultrasound radiating members are equivalent, the first ultrasoundradiating member 312 will have the full driving signal appearing acrossits terminals, six ultrasound radiating members 314, 316, 318, 320, 322,324 will have a half-strength driving signal appearing across theirterminals, and the remaining three ultrasound radiating members 326,328, 330 will have no voltage differential appearing across theirterminals.

FIG. 16 illustrates an embodiment wherein the pairs of switches for thefirst and third ultrasound radiating member driving lines 302, 306 arein the (closed, open) setting and the pairs of switches for theremaining ultrasound radiating member driving lines 304, 308, 310 are inthe (open, closed) setting. In this configuration, six ultrasoundradiating members 312, 316, 318, 320, 326, 328 are active, and theremaining four ultrasound radiating members 314, 322, 324, 330 areinactive.

FIG. 17 shows a modified catheter configuration with seven connectionsto the isolation pod 200. In such a configuration, the isolation pod 200uses four switches to connect the first terminal 278 of the drivingsignal to the first four ultrasound radiating member driving lines 352,354, 356, 358, and three switches to connect the second terminal 280 ofthe driving signal to the remaining three ultrasound radiating memberdriving lines 360, 362, 364. When all of the switches connected to thefirst terminal 278 are in the (closed) setting, each switch connected tothe second terminal 280 activates a bank of four ultrasound radiatingmembers. For example, if all the switches to the first terminal 278 areclosed, closing the switch for the ultrasound radiating member drivingline 360 activates four ultrasound radiating members 372, 378, 384, 390.Closing the switch for the ultrasound radiating member driving line 362activates four ultrasound radiating members 374, 380, 386, 392, andclosing the switch for the ultrasound radiating member driving line 364activates four ultrasound radiating members 376, 382, 388, 394. Thebanks are independently operable, so zero, one or two banks can beactive at any given time.

Alternatively, when all of the switches connected to the second terminal280 are in the (closed) setting, each switch connected to the firstterminal 278 activates a bank of three ultrasound radiating members. Forexample, if all the switches to the second terminal 280 are closed,closing the switch for the ultrasound radiating member driving line 352activates three ultrasound radiating members 372, 374, 376, 378. Otherbanks of three ultrasound radiating members are activated by the closingswitches for the remaining three ultrasound radiating member drivinglines 354, 356, 358. Again, the banks are independently operable, sozero, one, two, or three banks can be active at any given time.

It is not necessary to activate the ultrasound radiating members inbanks, because the switches can be individually controlled. A total of2⁷=128 driving combinations are possible. The non-bank configurationsinclude voltage divider circuits, so all of the ultrasound radiatingmembers are not driven at full strength in these configurations.

FIG. 18 illustrates another catheter embodiment where the ultrasoundradiating members are arranged in three banks with four ultrasoundradiating members in each bank. Closing the switch for ultrasoundradiating member driving line 430 activates four ultrasound radiatingmembers 402, 408, 414, 420. Closing the switch for ultrasound radiatingmember driving line 432 activates four ultrasound radiating members 404,410, 416, 422. Closing the switch for ultrasound radiating memberdriving line 434 activates four ultrasound radiating members 406, 412,418, 424.

One of ordinary skill in the art will understand that the illustratedembodiments are exemplary and that the catheter design is not limited tothe illustrated configurations. For example, the catheter may includedifferent numbers of ultrasound radiating members, ultrasound radiatingmember driving lines, or switches. Some or all of the switches mayalternately be included as part of the catheter.

A catheter may include ultrasound radiating members tuned to resonate atmultiple frequencies. Ultrasound radiating members having the sameresonant frequency can be selected individually or in groups.Alternatively, ultrasound radiating members having different resonantfrequencies can be driven by the same driving signal. In suchembodiments, the amount of ultrasonic energy delivered by an ultrasoundradiating member depends in part on the frequency at which theultrasound radiating member is driven.

Controlling the amplitude and frequency of the driving signal andarranging the placement of the ultrasound radiating members allows thecatheter to deliver appropriate ultrasonic energy levels to thetreatment site. In certain applications, it is desired that the catheterdelivers a uniform dose of ultrasonic energy to the treatment site. Inother applications, it is desired to deliver greater amounts ofultrasonic energy or ultrasonic energy of a different frequency todifferent portions of the treatment site. The individual control of theultrasound radiating members described above allows the ultrasoundassembly to deliver the appropriate amount and quality of ultrasonicenergy to the treatment site.

For example, piezoelectric transducers can be used to generateultrasonic energy. Piezoelectric transducers produce ultrasonic energywhen an electric voltage is applied to certain crystalline structures.The characteristics of the ultrasonic energy generated by apiezoelectric transducer is determined by the crystalline structure ofthe transducer, as well as by the frequency and voltage at which thetransducer is driven.

As shown in FIG. 12, the isolation pod 200 includes circuitry forcontrolling the generation of ultrasonic energy. In one embodiment, analternating current (“AC”) signal is provided to the isolation pod 200from an external source. In another embodiment, the AC signal isgenerated within the isolation pod 200 using circuitry such as a crystaloscillator. In one embodiment, the AC signal drives the ultrasoundradiating members directly. In a modified embodiment, the isolation pod200 includes additional circuitry to modify the AC signal before drivingthe ultrasound radiating members.

As discussed above, and as shown in FIG. 12, in certain embodiments thecatheter further comprises temperature sensors. As illustrated, thecurrent source applies a constant current bias across a silicon P-Ndiode junction. At a constant current bias, the voltage drop across asilicon P-N diode junction shows roughly a −2 mV ° C.⁻¹ temperaturecoefficient. The arrangement of temperature sensor diodes in thecatheter together with the diode path selection switches and thereversible current source allows the isolation pod 200 to select asingle diode from the set of twelve diodes for measuring thetemperature. The remaining diodes are either switched out of the circuitor reverse biased. A pre-amplifier circuit amplifies the voltage dropacross the diode and provides a signal to an analog to digital (A/D)converter.

FIG. 19 illustrates a diode arrangement within a catheter. In thisembodiment, configuring a first set of switches in the (open, closed)setting, a second set of switches in the (closed, open) setting, and theremaining to sets of switches in the (open, open) setting results in onediode being forward biased and a second diode being reverse biased. Theremaining diodes are left floating at one or both terminals. Thedirection of the current is controlled by a single-pull double-throw(SPDT) switch as illustrated in FIG. 12. The direction of the currentdetermines which of the two non-floating diodes is forward biased.

Because there may be some variance in the diodes when used astemperatures sensors, one embodiment utilizes a calibration process. Forexample, calibration data may be included in the ID PROM 254. Inmodified embodiments, the diodes can be calibrated against an ambienttemperature reading.

In other embodiments, the temperature sensors 20 monitor the temperatureof the treatment site at which the catheter is operating. For example,in one embodiment a temperature sensor is placed near a ultrasoundradiating member to measure the temperature of the tissue near thecatheter. In other embodiments, a temperature sensor is positionedbetween two ultrasound radiating members to measure the average energydelivered by the ultrasound assembly.

Referring again to the isolation pod 200 illustrated in FIG. 12, poweris provided through the power isolation transformer 276. Communicationsdata can be modulated with the power signal. For example, the embodimentillustrated in FIG. 12 further comprises a modulator/demodulator(“modem”) configured to transmit and receive signals modulated on thepower signal. This allows a microcontroller 272 to communicate with theexternal control circuitry 100. In such embodiments, the externalcontrol circuitry 100 can effectively control the activation ofultrasound radiating members and diodes by sending commands to themicrocontroller. Or, in modified embodiments, the microcontroller canexecute control sequences from memory. The microcontroller preferablyincludes outputs to control the switches and other drivers within theisolation pod 200.

Still referring to FIG. 12, a PROM 254 contains information relating toa number of factors, including but not limited to the catheter length,the number of ultrasound radiating members, the center frequency atwhich each ultrasound radiating member should be run, the tuningparameters for the ultrasound radiating members, and the calibrationfactors for the temperature sensors. A catheter connector 230,illustrated in FIG. 20, and which will be described in detail below,provides connection between the wires in the isolation pod 200 and thewires in the cable 45. These wires carry electrical signals between theisolation pod 200 and the inner core 34 located within the catheter 10.

As illustrated in FIG. 20, the connection between the isolation pod 200and the catheter 10 generally comprises a catheter connector 230. Thecatheter connector 230 is preferably integral with the isolation pod200, and generally comprises a customized slot 240 into which the cable45 fits. One advantage of having the catheter connector 230 integralwith the isolation pod 200 is the reduction in physical space and coststhat are associated with using an additional cable and connection deviceoutside the isolation pod 200. In the illustrated embodiment, atoe-catch arrangement assures a proper fit and assists in keeping theconnecting end of the cable 45 within the customized slot. The catheterconnector 230 preferably includes a latch 244 to secure the connectingend of the cable 45 within the customized slot 240.

Still referring to FIG. 20, the catheter connector 230 preferablycomprises an array of gold spring contacts 246 which provide anelectrical connection between the isolation pod 200 and the cable 45.The wire contacts at the connecting end of the cable are configured tobe aligned with the gold spring contacts 246 of the connector 230. Thecatheter connector 230, the cable 45, and their respective componentscan be manufactured in accordance with any of the variety of techniqueswell known in the electrical interfacing and wiring fields.

In the embodiment illustrated in FIG. 12, a catheter houses theultrasound radiating members and the temperature sensors. In suchembodiments, the catheter is connected to the isolation pod 200 whichhouses the electronics capable of driving the ultrasound radiatingmembers, as well as additional electronics capable of processingtemperature signals received from the catheter. In one embodiment, theisolation pod 200 receives control signals from external circuitry 300,and transmits data back to the external circuitry using a data interface252.

In another embodiment, all or part of the electronics for driving theultrasound radiating members is housed within the backend hub 33.Similarly, all or part of the electronics for processing the temperaturesignals is can be housed within the backend hub 33 as well. However,because certain catheters described herein are intended to bedisposable, the cost of the catheter can be reduced by minimizing theamount of electronics contained within the catheter. Additionally,reducing the amount of electronics contained within the catheter alsoreduces the catheter size. Thus, catheters configured to operate innarrow passages such as small vessels will also benefit from thereduction of electronics contained within the catheter. Therefore, inother embodiments, minimal electronics is incorporated within thecatheter.

A user may connect multiple types of catheters to a single isolation pod200. To identify the type of catheter connected to the isolation pod200, the catheter preferably includes electronics containing anidentifying code. The identifying code conveys information such as thetype of catheter, the serial number of the catheter, the manufacturinglocation of the catheter, the date of manufacture, or other identifyinginformation. In one embodiment, the circuitry for storing theidentifying code is a PROM 254. Other types of memory such as flashmemory or non-volatile random access memory (“RAM”) can also serve toidentify the catheter. Electronics such as switches, jumpers, diodes, orhard wired connections can also serve to identify the catheter. One ofordinary skill in the art will recognize that other circuits notdisclosed herein will also provide identification of the catheter.

Information contained on the identification PROM 254 can include, forexample, the length of the catheter, the length of the treatment zone,the number of ultrasound radiating members in the catheter, theultrasound radiating member layout, the resonant frequency of theultrasound radiating members, tuning information for the ultrasoundradiating members, compensation and/or calibration data for the diodes,or patterns for driving the ultrasound radiating members.

As illustrated in FIG. 12, in one embodiment, temperature sensitivediodes 238 are used as sensors to measure a temperature near thecatheter. In such embodiments, a pair of temperature sensitive diodes238 is selectively enabled, and an output signal is provided to ananalog to digital (“A/D”) converter. Or, in modified embodiments,multiple pairs of diodes are activated with the output signals beingprovided to the A/D converter simultaneously. Other embodiments includea sensor to measure the ambient temperature, which is used, for example,to calibrate the temperature sensors. Additionally, the ambienttemperature provides information as to whether the catheter andisolation pod are functioning properly.

Still referring to FIG. 12, the output of the A/D converter 270 isprovided to a microcontroller 272 for analysis. The microcontroller 272monitors the heat produced by the various ultrasound radiating membersand/or the temperature of the tissue near the catheter, and uses suchinformation to provide control signals to adjust characteristics such assignal strength or frequency of the driving signal provided to theindividual ultrasound radiating members.

One of ordinary skill in the art will recognize that the variousembodiments of the isolation pod described above, and illustrated inFIGS. 14 through 20, can be used with the catheter and variousultrasound radiating member and temperature sensor configurationsillustrated in FIGS. 2 through 8. In addition, the various embodimentsof the isolation pod described above, and illustrated in FIGS. 14through 20, can also be used with other ultrasound radiating member andtemperature sensor configurations not specifically described herein. Forexample, the isolation pod may also be used with an ultrasonic catheterthat has only one ultrasound radiating member and/or is configured tofit within the small vessels of the body such as the small vesselcatheters described in co-pending U.S. patent application, entitled“Small Vessel Ultrasound Catheter”, filed on the same date as thepresent application.

While the foregoing detailed description has described severalembodiments of the apparatus and methods of the present invention, it isto be understood that the above description is illustrative only and notlimited of the disclosed invention. It will be appreciated that thespecific dimensions of the various catheters and inner cores can differfrom those described above, and that the methods described can be usedwithin any biological conduit in a patient's body, while remainingwithin the scope of the present invention. Thus, the present inventionis to be limited only by the claims that follow.

1. An ultrasonic catheter system comprising: a tubular body having aproximal end, a distal end and a treatment zone located between thedistal end and the proximal end, a fluid delivery lumen; at least oneultrasound radiating element positioned in the treatment zone; wiringelectrically coupled to the at least one ultrasound radiating elementand extending through the tubular body and terminating at a connector;and a control system comprising external circuitry and an isolation podthat is configured to be electrically connected to the connector, theisolation pod being positioned between the tubular body and the externalsystem and comprising an isolation barrier and circuitry for driving theultrasound radiating element.
 2. The ultrasonic catheter system of claim1, wherein the external circuitry provides a radio frequency signal tothe isolation pod.
 3. The ultrasonic catheter system of claim 2, whereinisolation pod includes a transformer for converting the radio frequencyto a drive signal for driving the ultrasound radiating member.
 4. Theultrasonic catheter system of claim 1, wherein the isolation podincludes a transformer loop that is configured to measure leakagecurrent through the tubular body.
 5. The ultrasonic catheter system ofclaim 1, wherein the isolation pod includes tuning circuitry thatadjusts an input impedance based upon the activation of an ultrasoundtransducer.
 6. The ultrasonic catheter system of claim 1, wherein thecatheter ultrasonic assembly includes a plurality of ultrasonictransducers, and the control pod includes a selection matrix forselectively activating at least one group of the ultrasonic transducers.7. The ultrasonic catheter system of claim 6, wherein the group ofultrasonic transducers comprises more than one ultrasonic transducer. 8.The ultrasonic catheter system of claim 1, wherein the connectorincludes a memory device that stores information relating to thecatheter.